Reduce build sizes

[marcuswestin]

Current build sizes are a bit bigger than v1.

• Figure out sources of bloat (e.g do lots of modules add a bunch of boilerplate?)
• Consider trying other minifiers, e.g closure
• Compare gzipped sizes

[marcuswestin]

Also see #129

[marcuswestin]

• Consider removing non-shim implementations in util.js

[marcuswestin]

• Consider splitting up util.js to only keep functions store-engine.js depends on (for a minimal build)

[marcuswestin]

• consider not using util.js in store-engine.js

[marcuswestin]

• Consider splitting out plugin code into its own file, and not importing it in store.minimal.js

[marcuswestin]

• Allow uglifyjs to mangle property names (store.js v1 did much of this manually by using almost exclusively locally scoped variables instead of objects)
• Create a minimal build which doesn't depend on the browserify require module runtime, but uses minimal file concatenation of store-engine.js and a minimal-build.js.

[PaulBGD]

You could use rollup, since that can heavily improve the size of a bundle with treeshaking + putting everything in the same scope.

[marcuswestin]

@PaulBGD 👍👍 wasn't aware of rollup! Will check it out - thanks!